1. Field of the Invention
The present invention relates to an electronic circuit that supplies a supply voltage to a microprocessor such as CPU.
2. Description of the Related Art
A predetermined power supply voltage, which is stabilized by a power supply circuit such as a voltage regulator circuit, is supplied to CPUs, graphic processors and the like (hereinafter referred to collectively as “microprocessors”), which are used in personal computers, workstations, game machines and the like.
In the path supplying a power supply voltage to a microprocessor, a decoupling capacitor is provided between the power line and the grounding in order to remove noises occurring in the voltage regulator circuit or prevent the leakage to the outside of high-frequency noises occurring in the microprocessor. Noise removal by a decoupling capacitor is now a very important technology for stable operation of devices outfitted with a microprocessor or for the reduction of EMI (Electro-Magnetic Interference).
As a decoupling capacitor, a tantalum capacitor, an electrolytic capacitor or a ceramic capacitor is used generally. And several to several tens of decoupling capacitors, which are used on a printed-circuit board having a microprocessor, tend to occupy a considerable area. Also, the cost of surface-mounting a large number of decoupling capacitors can be significant.
Thus attempts are being made to use transmission line type noise filters instead of decoupling capacitors (See Reference (1) and Reference (2) in the following Related Art List, for instance). Such transmission line type noise filters are distributed constant filters, which are characterized by their capacity to remove noises over an extremely wide band.